Self-cleaning outdoor high-tension insulators



Jan. 1, 1957 van R0 2,776,332

SELF-CLEANING OUTDOOR HIGH-TENSION INSULATORS Filed June 25, 1952 2Sheets-Sheet 1 Jan. 1, 1957 H- VON CRON SELFCLEANIN QU'IDOORHIGH-TENSION INSULATORS Filed June 25, 1952 2 Sheets-Sheet. 2

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to Siemens-Schucltertwerke Aktiengeselischat't, Berlin- Siernensstadt,Germany, a corporation of Germany Application June 25, 1952, Serial No.295,523

6 Claims. (Cl. 174-411) My invention relates to outdoor high-tensioninsulators for electric transmission or distribution purposes and isdescribed hereinafter with reference to the drawings, in which:

Fig. 1 shows, partially in section, a high-tension overhead-lineinsulator of the known rain-shedding bell type;

Fig. 2 is a view partly in section of a rod-shaped insulator the anglebeing exaggerated and, in fact, being substantially zero in thepreferred form of the invention, as shown in Figs. 3a, 4 and 5;

Figs. 3a, 3b, and show respective cross-sectional modificationsapplicable to insulators according to the invention; and

Figs. 4 and 5 are respective views of two other insulators according tothe invention.

Outdoor insulators for high-tension lines are either of therain-shedding or of the self-cleaning type. The rain-shedding insulatorsare now being given an almost exclusive preference. The rain sheds orpetticoats of these insulators have such a shape and spread that a zoneunder each shed is kept dry from rain. In the rain, the voltage acrossthe insulator terminals is divided into a major portion across the dryzones, and a fractional portion across the wet insulator parts. Suchinsulators have the disadvantage that coats of dirt collecting upon thedry surface zones may in time become thick enough to appreciably reducethe flashover voltage of the insulator when a moisture film precipitatesdue to fog or dew. This is because the moisture on the dirt coatingdissolves conductive constituents of the dirt and thus greatly increasesthe conductivity of the moisture film. The resulting reduction infiashover voltage makes it necessary to clean the insulators morefrequently as the danger of dirt precipitation increases.

As an example of such an insulator, Fig. 1 shows a pin-type insulatorwith three sheds or petticoats. When installed, the insulator body 1 ofporcelain is supported on a metal pin 2,. The voltage is effectivebetween the pin 2 and the line mounted at 3 or supported by the topnotch or a top cap (not shown) of the insulator. The relatively largepetticoats of the insulator keep three surface zones dry from rain,these zones being schematically shown at ab, c-d and e in time, thickcoats of dirt may accumulate in these zones.

So far, vertical outdoor insulators of the self-cleaning type have foundonly rare application for high-tension lines. These self-cleaninginsulators have been used as strings of insulator units, each unithaving a metalcapped insulator disc joined with the adjacent unit by alink pin. In the rain, the underside of each disc is rinsed by the waterso that the entire insulator surface Patented Jan. 1, 1957 is washedclean. However, the distance between the discs of such an insulatorstring must be relatively large so that only a relatively small numberof discs can be accommodated on any given length (total fiashoverdistance) between the line electrode and the grounded electrode. Hence,the fiashover voltage is unfavorably small. it is an object of myinvention to provide a high-tension outdoor insulator of theself-cleaning type for installation in a vertical or approximatelyvertical position, which, when covered by a coherent moisture film dueto fog or dew, has a much higher fiashover voltage than heretoforeattainable with insulators of this type.

Another, ancillary object of my invention is to devise a self-cleaninginsulator which, for any given axial length, permits providing a largernumber of insulating disc-like projections thus greatly increasing theleakage distances.

Still another object of my invention is to make certain that even inheavy rain storms the leakage current along the insulator cannot assumeexcessive values due to water dripping from the disc edges, or due tothe formation of thick layers or streams of water especially on thelower part of the insulator surface.

An object of my invention is also to give the selfcleaning insulatorsuch a design that any coherent film of moisture formed during arainfall is thereafter rapidly heated and thereby disruptedsimultaneously at a large number of places.

According to a feature of my invention, a self-cleaning outdoorinsulator to be mounted in a vertical or approximately verticalposition, has an insulating trunk portion integral with disc-typeprojections which surround the trunk portion in form of a helix andwhich are rinsable by the rain water not only on the upper side but alsoon the underside of each helical turn. Thus, any accumulation of dirt iswashed Ofi in a manner comparable to the self-cleaning of theabove-mentioned known insulators. However, while the known insulators,if the rain impinges laterally as is generally the case, are cleanedmainly on the windward side, the helical turns of the disc-likeprojections in an insulator according to the invention distribute therain water also over the leeward side, thus securing a more uniformcleaning of the entire insulator surface.

These and other features and advantages of my invention will be apparentfrom, and will be referred to in, the following description of theembodiments of insulators according to the invention shown in Figs. 2 to5.

The insulator according to Fig. 2 has a trunk portion 10 and a disc-likeprojecting structure formed of an integral body of ceramic material suchas porcelain. The projecting structure consists of two helical turns 11and 12 extending around and along the trunk portion. The trunk portionmay be tubular as illustrated, or it may be given a solid design. Ineither case, the trunk has a uniform cross-section throughout itslength. The terminal electrodes 13 and 14 of the insulator are sunkeninto the ends of the trunk portion to minimize the electric fieldstrength at the edge of each electrode thus avoiding excessivedischarges as well as an electrostatic precipitation of dust. The pitchangle of the helical projection is designated by or. The axial crosssection of each individual turn of the projecting helix structure hasits top side inclined relative to the horizontal by an angle 5. Thecorresponding underside of the cross section is inclined an angle 7relative to the horizontal. The angles 5 and are hereinafter brieflyreferred to as the radial inclinations of the projecting surface, incontrast to the tangential inclination or pitch angle a. The inclinationa of the helix and the radial inclinations 8 and 'y of the contour aresuch that, in the rain, the entire surface of the insulator, i. e. alsothe undersides of the projections are rinsed by a substantially uniformveil of water. At the undersides, this veil need only be just sufficientfor eliminating any accumulated dirt or at least dissolving its solubleconstituents. The rain water caught by the helical projections thereforedivides itself into two portions. One portion flows vertically over thehelix edges in a quantity depending upon the radial inclinations andforms a more or less pronounced veil of water running downwardly alongthe insulator. The other, larger portion of the rain water collectingupon the insulator surface flows downwardly along the upper surfaces ofthe projections along the helical path formed thereby.

As mentioned, the individual insulator discs in the known self-cleaninginsulators for high-tension lines must have a large axial spacing fromeach other. This is because all of the rain water collected upon theinsulator must flow downwardly over the disc edges and thence tends toform thick rings and large drops of water at these edges. In contrast,the disc-like projections formed by the helical turns in an insulatoraccording to the invention may be given a narrow spacing from oneanother. This is possible because as mentioned, a large portion of thecollected rain water is immediately drained from the insulator along thehelical path so that only a small residual portion of water can flowover the edges and over the underside of the disc-like projections. Bythus providing a very large number of projections or discs along a givenaxial length or fiashover distance, the leakage distances are greatlyincreased. This is especially advantageous in humid weather resulting inthe formation of a coherent film of condensed moisture. The smallleakage current passing through the film has a heating effect which is amaximum at the surface points of the insulator trunk between thesuccessive helix turns. Since there is a large number of such places,the electric discharge that may occur at these places due to the heatingand disruption of the film are numerous and occur locally within narrowlimits. Under these conditions the electric discharges resulting fromthe disruption of the moisture film consume a relatively high voltageper unit of length. As a result, the leakage current is very stronglyreduced so that a fiashover along the entire arcing distance between theterminal electrodes of the insulator is safely prevented.

During rain storms, the stream of water draining oif along the helicalpath has a very large length compared with the axial length of theinsulator. Consequently, any leakage current that may then be flowingremains relatively small and can be interrupted without difficulty whenthe rain ceases. As mentioned above, the direct leakage path, on whichthe water runs vertically downward over the edges of the helical turns,is likewise relatively long. The formation of thick-layered runs ofwater in the longitudinal direction of the insulator that may directlyconnect one electrode with the other is prevented not only because alarge portion of the water drains off along the helix, but also becauseall water particles are given a tangential component of motion so thatthey can nowhere follow the strictly vertical direction of gravity.

When the rain ceases, preliminary discharges occur at the peripheraledges of the helical projections because the film of rain Water isthinnest and hence evaporates first at these places. The portion ofwater which drains along the helical path forms a shunt resistor to allthese locations of initial disiuption, and thus effects a substantiallyuniform voltage distribution over these locations. This prevents any ofthe individual discharges from growing into a fiashover between theterminal electrodes.

As mentioned, the helical projecting structure in the embodiment of Fig.2 is designed as a double-turn helix. This has the advantage that alarge number of individual turns or projections can be accommodatedwithin a given arcing distance, while giving the pitch angle a asatisfactorily large magnitude to impart to the run-off water acorrespondingly increased acceleration in the tangential direction. Forthe same reasons, more than two helical turns may be provided although,as apparent from Fig. 4, the helical projection may also be given asingle-turn design.

In order to secure the above-described results, the underside of eachhelical turn must slope continuously downward from the edge of the turnto the upper side of the next lower turn. The radial inclination "y ofthe underside of each projection should be at least 20, and preferablyabout 30. With such an inclination, the water runs in an approximatelyuniform layer thickness along the undersides of the projections towardthe trunk portion of the insulator.

The upper contour line of the axial cross section of each projectionshould not be given, at most, more than a slight angle of inclination 5relative to the horizontal. In the preferred form this angle is madezero so that the upper contour of each individual projection or turncross section has a horizontal direction. This is highly desirablebecause the amount of water accelerated along the helical path issubjected to centrifugal force which urges a small portion of the waterradially toward the edge of the helical projection. Thence, the waterflows in a thin coherent layer over the underside of the projection,this layer clinging closely to the insulator due to the strong adhesiveaction exerted by the insulator surface upon such a thin film of water.Hence, this small amount of water suflices to clean the insulator fromaccumulated dust also at the places not directly impinged upon by therain.

The radial spread distance of the disc-like projections from the trunkportion (smallest exterior diameter) of the insulator is preferably madeabout equal to the vertical spacing of respective points on theperiphery of two adjacent individual projections. Tests have shown thatsuch a dimensioning results in an insulator design of optimum qualties.

Since the quantity of the helically draining water increases from thetop toward the foot of the insulator, the upper contour line of theprojections may be given a concave shape in the lower part of theinsulator. In this manner, the quantity of the portion of water flowingover the edges downwardly along the direct leakage path of the insulatorcan readily be kept from assuming excessive magnitudes.

Figs. 3a, 3b and 3c show different profiles suitable for thus modifyingthe ratio of the helical run-0E to the over-edge portions of water inthe lower part of the insulator. In the upper portion of the helicalturns in an insulator designed, for instance, in accordance with Fig. 2,the upper contour line of the turn cross section is substantiallyhorizontal as shown at 11a in Fig. 3a. The turn portions in the middlepart of the insulator have a slightly concave contour line as shown at11b in Fig. 3b. In the turn-portions near the bottom of the insulatorthe corresponding contour line is more strongly concave as shown at inFig. 30.

Since the helical path of the water is considerably longer than thevertical path, the electrical resistance of the helical current passageis so high that only a small electric current can flow along the turnsof the helix. Such a small current can readily be interrupted and staysbelow the magnitude at which a fiashover may be ignited. The helicalwater path may be made longer by giving the trunk portion a largerdiameter or providing a singleturn helix. Due to the fact that, when therain ceases,

the water flowing downwardly over the shortest leakage distanceevaporates first at the helical edges because of the slight thickness ofthe water layer at these places, the current flow along the verticalleakage distance is first interrupted at the helical edges and at verymany individual places. Thereafter the helically flowing residualcurrent is also interrupted as the water drains ofi.

In dewy weather, fog or drizzle, the thin film of moisture firstevaporates at the points of the trunk between the turns of the helicalprojections, and glow discharges may occur at these places overindividual discharge distances of a very small length. Due to the highvoltage consumption of these series discharges, the leakage currentcannot reach a detrimental value, and a complete flashover fromelectrode to electrode is prevented.

For promoting the simultaneous disruption of the moisture film at manydispersed places, a helical heating conductor may be provided on orbetween the turns of the projecting structure so as to helicallysurround the trunk portion of the insulator. The heating conductor mayconsist of a strip-shaped surface glaze of electrically resistive orsemi-conductive properties. Such a glazed strip may be provided, forinstance, along the peripheral edge of the projections or on the trunkportion between the projecting turns.

The insulators illustrated in Figs. 4 and 5 embody the above-mentionedfeatures. The trunk portion of the insulator shown in Fig. 4 is integralwith a projecting structure 11 which forms a single-turn helix. As canbe readily seen, the trunk has a uniform cross-section throughout itslength. The axial ends of the insulator are recessed to receiverespective portions of the terminal electrodes 13 and 14. A helicalheating conductor is disposed on the edge of the projecting structure 11and consists of a semiconductive glaze of small width. The ends of theglazed strip are conductively joined with the respective terminalelectrodes 13 and 14 so that the glazed conductor 15 is traversed by aslight current when the insulator is under voltage. By virtue of theillustrated insulator design, the peripheral edge of the helicalprojection can be brought up to a locally raised temperature by means ofa very small heating current flowing through the conductor 15, thisbeing possible because the mass and heat capacity of the edge portion issmall in comparison with the mass of the insulator trunk portion. Theheating efiect of the conductor 15 aids materially in rupturing themoisture film at very many places along the extended helical course ofthe projecting edge.

The insulator illustrated in Fig. 5 is equipped with two helicalprojecting structures 11 and 12 and, in this respect, is similar to theabove-described insulator of Fig. 2. Connected with the terminalelectrodes 13 and 14 are two heating conductors 16 and 17 which extendhelically around the trunk portion between the adjacent turns of thedouble-turn helix, following the smallest exterior diameter of theinsulator body.

Insulators according to the invention may be used or designed assuspension insulators, as supporting insulators in open air stations, aslead-in insulators and entrance bushings for outdoor installation, asarc chambers of out-door power breakers, as terminal bushings fortopconnected outdoor breakers, as an enclosure of overvoltage protectorsor measuring transformers, as an insulating bushing for bushing-typecurrent transformers, and other outdoor purposes requiring an insulatingstructure to be mounted in a vertical or approximately verticalposition.

I claim:

1. An outdoor insulator of the self-cleaning type for vertical orapproximately vertical mounting, comprising an elongated rod-shapedtrunk portion and a projecting structure both of insulating material andintegral with each other, said structure having helical turns around andalong said trunk portion, each turn having a vertical cross sectionwhose upper edge is substantially horizontal and whose underside edgehas a continuously downward slope from the periphery down to the upperside of the next lower turn, and heating conductor means of helicalshape joined with the insulator and forming a helix coaxial with saidtrunk portion.

2. An outdoor insulator of the self-cleaning type for vertical orapproximately vertical mounting, comprising an elongated rod-shapedtrunk portion and a projecting structure both of insulating material andintegral with each other, said structure having helical turns around andalong said trunk portion, each turn having a vertical cross sectionwhose underside edge has a continuously downward slope from theperiphery down to the upper side of the next lower turn, two conductiveterminals mounted on the respective axial ends of said trunk portion,and heating resistor means electrically connected between said terminalsand forming a helix coaxial with said trunk portion.

3. An outdoor insulator of the self-cleaning type for vertical orapproximately vertical mounting, comprising an elongated rod-shapedtrunk portion and a projecting structure both of insulating material andintegral with each other, said structure having helical turns around andalong said trunk portion, each turn having a vertical cross sectionwhose upper edge is substantially horizontal and whose underside edgehas a continuously downward slope from the periphery down to the upperside of the next lower turn, two conductive terminals mounted on therespective axial ends of said trunk portion, and heating resistor meanselectrically connected between said terminals and extending along theperipheral edge of said helical projecting structure.

4. An outdoor insulator of the self-cleaning type for substantiallyvertical mounting, comprising an elongated trunk portion having auniform cross-section throughout its length and a projecting structure,both of insulating material and integral with each other, said structurehaving plural helical turns around and along said trunk portion, eachturn having a cross-section whose underside has a continuously downwardslope from the periphery down to the upward side of the next lower turn,and heating conductor means of helical shape joined with the insulatorand forming a helix coaxial with, and following the smallest exteriordiameter of, the trunk portion.

5. An outdoor insulator of the self-cleaning type for vertical orapproximately vertical mounting, comprising an elongated circular trunkportion having a uniform cross-section throughout its length, and aprojecting structure, said trunk portion and said structure being bothof insulating material and integral with each other, said structurehaving helical turns around and along said trunk portion, each turnhaving a vertical cross section whose upper edge is substantiallyhorizontal and whose underside edge has a continuously downward slopefrom the periphery down to the upper side of the next lower turn, sothat, when the insulator is mounted and exposed to rain, the upper sidesas well as the undersides of said helical turns are rinsed by rainwater, said trunk portion and said projecting structure consisting of aceramic body, said insulator having an electrically semiconductivesurface glaze forming a helical and coaxial heater strip along theinsulator.

6. An outdoor insulator of the rain self-cleaning type for vertical orapproximately vertical mounting, comprising an elongated trunk portionhaving a projecting structure, said trunk portion and said structurebeing both of insulating material and integral with each other, saidstructure comprising a helix coiled around and along said trunk portionproviding a helical ledge forming a path for rain water, the ledgeproviding a vertical cross section whose upper edge is substantiallyhorizontal whereby a small portion of the water is urged radiallyoutward by centrifugal force, the underside of each turn having acontinuously downward slope from the periphery down to the upper side ofthe next lower turn, so

that, when the insulator is mounted and exposed to rain, the undersideof said helix is rinsed by said small portion of rain water, said upperhorizontal cross-sectional edge of the ledge being in the upper portionof the insulator, the middle portion and the lowermost portion havingupper surfaces which are concave viewed downwardly, the lowermostportion having a more greatly concave surface than the middle portion,to modify the ratio of the water run-01f along the helical path to therun-off over the edge of the helical ledge.

References Cited in the file of this patent UNITED STATES PATENTSFOREIGN PATENTS Switzerland Dec. 31, 1907

